Steel



, HESS.

. Patented Aug. 19, 1941- Westinghouse Electric & Manufacturing Company,East Pittsburgh, Pa., a corporation of Pennsylvania No Drawing.Application January 29, 1941, Serial No. 376,420

, Claims. (01. 75-128);

Thisinvention relates to articles of manufacpressing and permanentmolding operations.

. Toolsteel employed heretofore as dies for hot pressing and permanent:molding operations where the tool is repeatedly heated at temperaturesof more than 1000 F. have failedin a relatively short time by cracking,warping or washing. In general, it can be said that while the steels ofpreviously known compositions have high hardness at elevatedtemperatures, they particularly to intergranular oxidation, to have along life. Intergranular oxidation results in development of points ofstress concentration which cause surface cracking. Surface cracks thedie .or mold.

Tool steels with high tungsten contents have long been known to possessvery high red hardness, that is, high hardness at relativelyhightemperatures. Likewise steels with high chromium contents have beenknown to possess high resistance to oxidation at relatively hightemperatures together with moderately high red hard- The high tungstensteels have never been "ture and particularly to steel suitablefor hotbined in a steel in relatively high proportions, a steel is producedhaving a toughness, hardness and resistance to oxidation which rendersit suitablefor use as a die for hot pressing and permanent moldingoperations at repeated high temperatures.

.are not sufliciently resistant to oxidation, and

' grow inwardly and ultimately lead to failure of consideredoxidation-resistant and therefore have usually been limited. in use toapplications where temperatures inservice do not exceed a temperature ofapproximately 1200 F.

Contact surfaces oi'dies and molds used for hot pressing and molding orcasting, particularly of non-ferrous metals and alloys probably reachtemperatures well in excess 0f l000 F. At these higher temperatures,ordinary tool steels containing high tungsten but relatively lowchromium contents do not possess adequate oxidation resistance. On theother hand, previously.

known high chromium steels with relatively low contents of otherhardening elements do not possess red hardness for most toolapplications.

It is an object of this invention, therefore, to provide a steel havinga high hardness at elevated temperatures, together with resistance tooxidation.

Another object of this invention is to provide a alloys.

characteristics desired in' a die, the steel may be subjected to a heattreatment, preferably after steel having a. high tungsten and a highchromium content which will have a high hardness at elevatedtemperatures together with resistance to oxidation.

Other objects of this invention will become apparent from the followingdescription and the The following table sets forth the broad ranges inpercent by weight within which the several a1- loying elements may bepresent:

Percent Carbon 0.05 to 0.50 Manganese 0.15 to 3.00 Silicon 0.20 to 1.00Chromium 8.00 to 20.00 Tungsten l 8.00 to 20.00 Vanadium; 0.10 to 4.00

th remainder being substantially all iron, together with such alloyingimpurities as are sometimes found in alloy steels.

A somewhat narrower range of percentages in which the several alloyingelements may be present are as follows Percent Carbon. 0.05 to 0.30Manganese 0.15 to 0.50 Silicon 0.20 to 0.50 Chromi m 11.00 to 15.00Tungsten 11.00 to 15.00 V n m 0.10 to 1.00

the remainder being substantially all iron, to gether with such alloyingimpurities asare sometimes found in alloy steels.

Steels having the composition given in the foregoing tables are found tobe satisfactory when formed into dies for hot pressing and permanentmolding operations, and particularly such operations on hot non-ferrousmetals and In order to give the steel certain of the having been formedto thepredetermined shape of the die. Where desired, the finishing ofmachining operations may be applied "to the die after the heattreatment.

The heat treatment may comprise quenching the steel in oil or air from atemperature between 2100? F. and 2350 F. and then subjecting it to atempering treatment at a temperature between 1100 F. and 1300 F. for asuflicient period of time to develop its hardness. A preferred heattreatment is to quench the steel from a temperature between 2250 F. and2300 F. and temper it at a temperature of about 11200 F'.

In making the steel-for forming the dies, it is Percent Percent PercentPercent Percent Carbon 25 20 20 24 l2 Manganese.. .25 .16 .27 .28 .25Silicon 25 21 36 38 25 Chromium 12. 12. l3 12. 02 12. 60 12. 00Tungsten- 8. 00 12. 71 12. 62 12. 89 12. 00 Vanadium-..- .50 .46 .43 .43.50

it being understood that the remainder of the composition of each of thespecific examples given is substantially all iron together with suchalloying impurities as are sometimes found in alloy steels.

As previously stated, it is found that the high chromium and hightungsten constituents cooperate to impart high red hardness and highoxidation resistance to the finished product. The vanadium and siliconconstituents function primarily as deoxidants in the making of the steeland the vanadium is thought to impart resistance in the steel againstgrain coarsening during the heat treatment of the alloy. The highercontents of vanadium may also assist in developing red hardness. Themanganese is thought to impart forgeability characteristics to thealloy. For most of the applications embodied by this invention, thelower carbon contents as set forth are thought to develop adequatehardness and to aid in obtaining a steel having greater toughness thanwould be obtained with the higher carbon contents. However, it is notdesired to be limited in application of the principles herein set forthto the lower carbon contents.

Dies formed from high chromium and high tungsten steel referred tohereinbefore are found to be resistant to oxidation. checking, warpingand washing. These dies may have a useful life of from twelve to fifteentimes the life of the dies formed from the conventional high tungsten,low chromium steels such as, for example, the tungsten, 3% chromium, 50%carbon, and .50%

vanadium steel available on the market at the present time whensubjected to operations entailing the repeated heatings at temperaturesof over 1000 F. The high chromium, high tungsten steel dies of thisinvention are particularly useful in the hot pressing of copper partsand permanent molding of aluminum bronzes.

I claim as my invention:

1. A tool steel suitable for hot pressing and permanent moldingoperations formed from an alloy composed of 8% to 20% chromium, 8% to20% tungsten, 0.10% to 4% vanadium, 0.20% to 1% silicon, 0.15% to 3%manganese, 0.05% to 0.5% carbon and the balance substantially all iron.

2. A toolsteel suitable for hot pressing and permanent moldingoperations formed from an alloy composed of 11% to 15% chromium, 11% to15% tungsten, 0.10% to 1% vanadium, 0.2% to 0.5% silicon, 0.15% to 0.5%manganese, 0.05% to 0.3% carbon and the balance substantially all iron.

3. A tool steel suitable for hot pressing and permanent moldingoperations formed from an alloy composed of about 12.62% chromium, about12.62% tungsten, about 0.43% vanadium, about 0.36% silicon, about 0.27%manganese, about 0.20% carbon and the balance substantially all iron.

4. A tool steel suitable for hot pressing and permanent moldingoperations comprising an alloy composed of 8% to 20% chromium, 8% to 20%tungsten, 0.10% to 4% vanadium, 0.20% to 1% silicon, 0.15% to 3%manganese, 0.05% to 0.5% carbon, and the balance substantially all ironformed to a predetermined shape and heat treated to give high hardness,the steel being characterized in that it is resistant to oxidation.

5. A tool steel comprising an alloy of 8% to 20% chromium, 8% to 20%tungsten, 0.10% to 4% vanadium, 0.20% to 1% silicon, 0.15% to 3%manganese, 0.05% to 0.5% carbon and the balance substantially all ironwhich has been quenched from a temperature between 2100 F. and 2350 F.and tempered at a temperature between 1100" F. and 1300 F.

